The long term objective of this research is to understand the genetic control of cell fate specification in the developing central nervous system (CNS) of Drosophila. This model system will hopefully provide a paradigm for studying the development of the much more complicated vertebrate CNS, and give us insights into how hereditary defects can lead to human neurological disease. We will study the function of the Drosophila gooseberry (gsb) gene which has been shown to be both necessary and sufficient to specify a number of neuronal cell fates. Antibodies will be made to the protein product of the gsb gene and its pattern of distribution determines within the CNS. The gsb protein contains a homeobox, and therefore, is probably a DNA binding protein which regulates the expression of other genes. The target sites in Drosophila DNA which bind the gsb protein will identified and the corresponding genes cloned. In this way, the genetic pathway of cell fate specification in the CNS can be elucidated. The last set of experiments will address the relation of cell lineage to the pattern of gsb protein expression within the CNS. A cell marking system will be developed for following cell lineages within the CNS. This marking system will be used to compare various patterns of protein expression to cell lineage and for making mosaics laking specific gene functions.